1. Field of the Invention
This invention generally relates to a linear motion rolling contact guide unit, and, in particular, to a such a linear motion rolling contact guide unit having an improved retainer plate for retaining rolling members.
2. Description of the Prior Art
A linear motion rolling contact guide unit is well known in the art, and it generally includes a rail 1, a slider 20 slidably mounted on the rail 1 and a plurality of rolling members 4 interposed between the rail 1 and the slider 20 to thereby provide a robing contact between the rail 1 and the slider 20 as shown in FIG. 6 . The guide unit shown in FIG. 6 is a so-called infinite stroke type and thus a pair of endless circulating path, each including a load path section; a return path section and a pair of curved connecting path sections each connecting the corresponding ends of the load and return path sections, is provided in the slider 20, thereby allowing to provide an infinite relative linear motion between the rail 1 and the slider 20 theoretically.
As shown in FIG. 6 , the rail 1 is generally rectangular or square in cross section and thus it includes a pair of opposite side surfaces 11, each of which is formed with an inner guide groove 9 extending in parallel with the longitudinal axis of the rail 1. The slider 20 has a generally U-shaped cross section and thus it generally includes a horizontal section and a pair of vertical sections each depending from a corresponding side of the horizontal section. Thus, the slider 20 is slidably mounted on the rail 1 in a straddling manner. In the example shown in FIG. 6 , the slider 20 has a three part structure: a center block 2 and a pair of front and rear end blocks 5, each located at each end of the center block 2. The center block 2 is often referred to as a casing and the end block 5 as a side cap in this field of technology.
The main reason why the slider 20 is comprised of such three parts is because each section of the endless circulating path is formed in a corresponding part. That is, the center block 2 is formed with an outer guide groove 8 which is located opposite to and in parallel with the associated inner guide groove 9 of the rail 1 to thereby define a load path section between the paired inner and outer guide grooves 9 and 8. The center block 2 is also formed with a return path section 36 which extends in parallel with the load path section 8-9. On the other hand, each of the end blocks 5 is formed with a curved connecting path section connecting the corresponding ends of the load and return path sections to thereby define an endless circulating path.
A plurality of rolling members 4, e.g., balls or rollers, are provided in each of the endless circulating paths, some of those balls 4 that are located in the load path section are shown in FIG. 6 . Thus, the balls 4 that are located in the load path section provide a rolling contact between the rail I and the slider 20. Since the balls 4 may roll indefinitely along the associated endless circulating path, a theoretically indefinite relative motion may be provided between the rail 1 and the slider 20 as long as the rail 1 extends.
The end block 5 is typically provided with an end seal member 19 for providing a sliding seal between the rail 1 and the slider 20 and also with a grease nipple 18 for supplying a lubricant to a sliding interface between the rail 1 and the slider 20 through a lubricant passage formed in the slider 20. In addition, the slider 20, in particular its center block 2 is provided with a holder band 17 which extends in parallel with and spaced apart from the outer guide groove 9 so as to hold the balls 4 in a spaced defined by the outer guide groove 9 and thus to prevent the balls 4 from falling off when the slider 20 is disassembled from the rail 1. Thus, the holder band 17 is located inside and near the valley of the inner guide groove 9 when the slider 20 is assembled with the rail 1 as best shown in FIG. 7.
Moreover, the center block 2 is also provided with a retainer plate 3 for further assuring to prevent the balls 4 from falling off the center block 2 and also for providing a seal between the center block 2 and the side surface 11 of the rail 1 and also at a bottom surface of the center block 2. FIGS. 7 and 8 illustrate a typical prior art retainer plate 3 which is described in the Japanese Pat. Laid-open Pub. No. 64-112021 which was assigned to the assignee of this application. As shown in FIGS. 7 and 8, the retainer plate 3 includes a first seal section 7 which extends somewhat aslant downward in the form of a lip, a second seal section 10 which extends horizontally and defines a seal surface at its top surface 21, and a retaining section 6 which extends vertically upward for holding the roiling members at its top end. And, these first and second seal sections 7 and 10 and the retaining section 6 are integrally formed from the same material, preferably a resin material.
In the illustrated example, the retainer plate 3 is fixedly attached to the center block 2 by bringing its top surface 21 in contact with a bottom surface 12 of the center block and inserting and tightening a screw 16 into a threaded hole in the center block through a through-hole 15 formed in the retainer plate 3. In this case, those balls in the outer guide groove 8 are retained in the center block 2 by the retaining section 22 of the retainer plate 3 arranged in contact with a side surface 22 of the center block 2 and also by the holder band 12 which is fixedly attached to the center block 2 at its opposite ends. In the structure shown in FIG. 7, a distance between a top edge 23 of the outer guide groove 8 and a top end surface 14 of the retaining section 22 of the retainer plate 3 is set to be larger than the diameter of the ball 4 so as to allow the ball 4 to roll along the load path section defined between the outer and inner guide grooves 8 and 9. However, a spacing between the holder band 13 and the top end surface 14 of the retaining section 6 is set to be smaller than the diameter of the ball 4 so as to prevent the ball 4 from slipping away from the outer guide groove 8.
In the structure shown in FIG. 7, each of the outer and inner guide grooves 8 and 9 has a generally V-shaped cross section deftned by a pair of curved, or circular, guide surfaces so as to provide an increased load bearing capability as compared with a pair of flat guide surfaces. Furthermore, as shown in FIG. 7, a top edge of the outer guide groove 8 is located at the side of the rail 1 with respect to a hypothetical vertical line passing through the center of the ball 4 in contact with the outer guide groove 8, and a bottom edge of the outer guide groove 8 is located at the side of the center block 2 with respect to the vertical line. Thus, a larger gap is provided between the side surface 11 of the rail 1 and the lower side surface 22 of the center block 2 as compared with a gap between the side surface 11 and an upper side surface of the center block 2 above the outer guide groove 8. This allows the retaining section 6 of the retainer plate 3 to be located between the opposed side surfaces 11 and 22.
As described before, the retainer plate 3 is preferably comprised of an elastic material, such as a plastic or resin material in a unitary structure, for example, by injection molding. Since the lip-shaped first seal section 7 is in sliding contact with the side surface 11 and the retaining section 6 is in contact with the side surface 22 of the center block 2, the gap between the rail 1 and the center block 2 is effectively sealed. Moreover, since the second seal section 10 is fixedly attached to the bottom surface 12 of the center block 2, the bottom surface 12 of the center block 2 is effectively sealed.
However, in the above-described prior art linear motion rolling contact guide unit, since the retainer plate 3 is fixedly attached to the center block 2 by means of screws 16, when the retainer plate 3 has become swelled because of impregnation of grease or oil, for example, after a long period of time, the retainer plate 3 becomes deformed. As a result, the sealing condition of the retainer plate iS deteriorates. For example, the first seal section 7 may be separated away from the side surface 11 and/or a gap is provided at an interface be tween the second seal section 10 and the bottom center block 2. Then undesired foreign matter and/or dust may sneak into the interior of the guide unit and cause an increase in the sliding resistance. In addition, the retaining section 6 of the retainer plate 3 may also be deformed to increase the spacing between the holder band 13 and the top end surface 14 of the retaining section 6, and, as a result, the balls 4 may fall off when the slider 20 is disassembled from the rail 1.